The present invention relates to fiber reinforced resin matrix composites, and more particularly, to a method facilitating the manufacture thereof which assures that each composite layer is properly oriented.
A rotor blade spar is the foremost structural element of a helicopter rotor blade assembly inasmuch as its primary function is to transfer combined flapwise, edgewise, torsional and centrifugal loads to/from a central torque drive hub member. The spar typically extends the full length of the rotor blade and mounts at its inboard end to a cuff assembly or fitting which facilitates mounting to the hub member. Due to the extreme operational loading environment of the rotor blade, fiber reinforced resin matrix composite materials, e.g., Kevlar, graphite and fiberglass, have been employed due to their advantageous strength to weight ratio, corrosion resistance, and improved damage tolerance.
To maximize the benefits of composites it is essential that the fiber orientation be optimally tailored to meet the strength and stiffness requirements for a particular application. That is, composites can be tailored to be anisotropic (capable of carrying load in a particular direction) rather than quasisotropic (equal strength in all directions); hence, orienting the fibers in the direction of the load will optimally result in the most weight efficient structure.
These considerations must be balanced against the cost and complexity of a particular fabrication technique. One technique for manufacturing composite components includes prepreg lay-up of composite materials. The prepreg lay-up technique employs the use of discrete plies or layers of pre-impregnated composite fabric, which are hand-stacked and interleaved over a mandrel assembly. The mandrel assembly is placed in a matched metal mold and cured in an autoclave oven for application of heat and pressure.
As described above, to assure the desired strength is achieved, the fiber orientation of each discrete laminate must be assured. This process is extremely time and labor intensive. Because many layers must be hand stacked, and each layer must be properly oriented during the hand lay-up process, there is a relatively high probability of operator error, e.g., an operator may inadvertently omit a layer in a multi-ply laminate or fail to properly orient one or more layers. The critical nature of this laborious hand lay-up process is such that a quality assurance inspector typically observes an operator during the process to assure no errors are made.
Accordingly, it is desirable to provide a method facilitating the manufacture of a composite structure which assures that each composite layer is properly oriented while minimizing the necessity of additional quality assurance personnel.
A fiber orientation verification system according to the present invention provides a sensor and an indicator above a lay-up surface such that each has a view of the lay-up surface. The sensor is preferably a digital camera to identify the fiber orientation within each sequentially laid composite material layer. In one embodiment, each composite material layer includes a contrasting strand which is readily identifiable. The indicator is preferably a laser projector which projects visible indicator lines upon the lay-up surface to indicate a desired orientation for the composite material layer.
The sensor and the indicator communicate with a computer module which contains a database including a detailed sequence of composite material layers, fiber orientation, indicator display programs, quality assurance and operator interfaces to assure that each layer is proper placed as described below.
The computer module initially refers to a desired database to obtain a sequence of composite material layers and fiber orientation of the desired composite component to which the system will verify. In response to the particular database, the computer module communicates with the indicator to project a plurality of visible indicator lines upon the lay-up surface. The indicator also projects an outline of the first composite material layer such that the operator is provided with a guide for accurate placement. The operator is thereby provided with an exact location to lay-up the first composite material layer and the proper fiber orientation of that layer. The display also indicates to the operator which step he is currently performing and confirmation as to the proper composite material layer type for that step, e.g. fiberglass, Kevlar, carbon fiber, or the like. Continued verification is thus preferably continually provided to the operator.
Once the operator positions a composite material layer, the computer module communicates with the sensor to identify the fiber orientation of that layer. The CPU compares the sensed fiber orientation to the proper orientation contained in the database for that particular step. Once the fiber orientation is determined, the CPU identifies whether the sensed fiber orientation is equivalent to the predetermined fiber orientation for that particular step. If the operator has properly positioned the composite material layer, the CPU moves to the next step (next lay-up layer) in the database. This process continues until the lay-up is complete.
Should, however, the operator fail to properly position or orient a composite material layer, the CPU will identify the incorrect layer and provide an alert to the operator. The operator is thereby alerted to the improper step, provided with the proper indicator lines and outline while being prevented from proceeding to the next layer.
The present invention therefore provides a system and method which facilitates the manufacture of a composite structure which assures that each composite layer is properly oriented while minimizing the necessity of additional quality assurance personnel.